ULTRAVIOLET (UV) is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays . UV radiation constitutes about 10% of the total light output of the Sun, and is thus present in sunlight . It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps , tanning lamps , and black lights . Although it's not considered an ionizing radiation because its photons lack the energy to ionize atoms , long-wavelength ultraviolet radiation can cause chemical reactions and causes many substances to glow or fluoresce . Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
Suntan , freckling and sunburn are familiar effects of over-exposure,
along with higher risk of skin cancer . Living things on dry land
would be severely damaged by ultraviolet radiation from the
Ultraviolet rays are invisible to most humans, although insects, birds, and some mammals can see near-UV.
* 1 Visibility * 2 Discovery * 3 Subtypes * 4 Solar ultraviolet * 5 Blockers and absorbers
* 6 Artificial sources
* 6.1 "Black lights" * 6.2 Short-wave ultraviolet lamps * 6.3 Gas-discharge lamps * 6.4 Ultraviolet LEDs * 6.5 Ultraviolet lasers * 6.6 Tunable vacuum ultraviolet (VUV) via sum and difference frequency mixing * 6.7 Plasma and synchrotron sources of extreme UV
* 7 Human health-related effects
* 7.1 Beneficial effects
* 7.2 Harmful effects
* 7.2.1 Skin damage
* 7.2.2 Aggravation of certain skin conditions * 7.2.3 Eye damage
* 8 Degradation of polymers, pigments and dyes
* 9 Applications
* 9.1 Photography * 9.2 Electrical and electronics industry * 9.3 Fluorescent dye uses
* 9.4 Analytic uses
* 9.4.1 Forensics * 9.4.2 Enhancing contrast of ink * 9.4.3 Sanitary compliance * 9.4.4 Chemistry
* 9.5 Material science uses
* 9.6 Biology-related uses
* 9.6.1 Air purification * 9.6.2 Sterilization and disinfection * 9.6.3 Biological * 9.6.4 Therapy * 9.6.5 Herpetology
* 10 Evolutionary significance * 11 See also * 12 References * 13 Further reading * 14 External links
Ultraviolet rays are invisible to most humans: the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, and people with aphakia (missing lens) or replacement lens can also see some UV wavelengths. Near-UV radiation is visible to insects, some mammals, and birds . Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.
UV radiation was discovered in 1801 when the German physicist Johann
Wilhelm Ritter observed that invisible rays just beyond the violet end
of the visible spectrum darkened silver chloride -soaked paper more
quickly than violet light itself. He called them "oxidizing rays" to
emphasize chemical reactivity and to distinguish them from "heat
rays", discovered the previous year at the other end of the visible
spectrum. The simpler term "chemical rays" was adopted shortly
thereafter, and it remained popular throughout the 19th century,
although there were those who held that these were an entirely
different sort of radiation from light (notably
John William Draper ,
who named them "tithonic rays" ). The terms chemical and heat rays
were eventually dropped in favour of ultraviolet and infrared
radiation , respectively. In 1878 the sterilizing effect of
short-wavelength light by killing bacteria was discovered. By 1903 it
was known the most effective wavelengths were around 250 nm. In 1960,
the effect of ultraviolet radiation on
The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann .
The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO-21348:
NAME ABBREVIATION WAVELENGTH (NM) PHOTON ENERGY (EV, AJ) NOTES / ALTERNATIVE NAMES
Ultraviolet A UVA 315–400 3.10–3.94, 0.497–0.631 Long-wave, black light , not absorbed by the ozone layer
Ultraviolet B UVB 280–315 3.94–4.43, 0.631–0.710 Medium-wave, mostly absorbed by the ozone layer
Ultraviolet C UVC 100–280 4.43–12.4, 0.710–1.987 Short-wave, germicidal , completely absorbed by the ozone layer and atmosphere
Near ultraviolet NUV 300–400 3.10–4.13, 0.497–0.662 Visible to birds, insects and fish
Middle ultraviolet MUV 200–300 4.13–6.20, 0.662–0.993
Far ultraviolet FUV 122–200 6.20–12.4, 0.993–1.987
Vacuum ultraviolet VUV 10–200 6.20–124, 0.993–19.867 Strongly absorbed by atmospheric oxygen, though 150–200 nm wavelengths can propagate through nitrogen
Extreme ultraviolet EUV 10–121 10.25–124, 1.642–19.867 Entirely ionizing radiation by some definitions; completely absorbed by the atmosphere
A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Many approaches seek to adapt visible light-sensing devices, but these can suffer from unwanted response to visible light and various instabilities. Ultraviolet can be detected by suitable photodiodes and photocathodes , which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are available. Spectrometers and radiometers are made for measurement of UV radiation. Silicon detectors are used across the spectrum.
People cannot perceive UV directly, since the lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea . Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as aphakia ) perceive near-UV as whitish-blue or whitish-violet.
Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths of about 150–200 nm can propagate through nitrogen . Scientific instruments can therefore utilize this spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers. Significant examples include 193 nm photolithography equipment (for semiconductor manufacturing ) and circular dichroism spectrometers.
Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.
Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30 nm interact mainly with the outer valence electrons of atoms, while wavelengths shorter than that interact mainly with inner-shell electrons and nuclei. The long end of the EUV spectrum is set by a prominent He+ spectral line at 30.4 nm. EUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50% of EUV radiation at normal incidence . This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and has been used to make telescopes for solar imaging. Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. In essence, all UVC is blocked by diatomic oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone, and most of it reaches the ground. UVA makes up almost all of the ~ 25% of the Sun's total UV that penetrates the Earth's atmosphere.
Very hot objects emit UV radiation (see black-body radiation ). The
However, at ground level sunlight is 44% visible light, 3%
ultraviolet (with the
The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air.
BLOCKERS AND ABSORBERS
Ultraviolet absorbers are molecules used in organic materials (polymers , paints , etc.) to absorb UV radiation to reduce the UV degradation (photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary.
In sunscreen , ingredients that absorb UVA/UVB rays, such as avobenzone , oxybenzone and octyl methoxycinnamate , are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as titanium dioxide and zinc oxide .
For clothing, the
Ultraviolet Protection Factor (UPF) represents the
ratio of sunburn -causing UV without and with the protection of the
fabric, similar to SPF (
Suspended nanoparticles in stained glass prevent UV rays from causing
chemical reactions that change image colors. A set of stained glass
color reference chips is planned to be used to calibrate the color
cameras for the 2019
Common soda lime glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas fused quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.
Wood\'s glass is a nickel-bearing form of glass with a deep blue-purple color that blocks most visible light and passes ultraviolet.
Two black light fluorescent tubes, showing use. The longer tube is a F15T8/BLB 18 inch, 15 watt tube, shown in the bottom image in a standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12 inch, 8 watt tube, used in a portable battery-powered black light sold as a pet urine detector. Main article: Blacklight
A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple Wood\'s glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometres. Others use plain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating. A black light may also be formed, very inefficiently, by using a layer of Wood's glass in the envelope for an incandescent bulb. Though cheaper than fluorescent UV lamps, only 0.1% of the input power is emitted as usable ultraviolet radiation. Mercury-vapor black lights in ratings up to 1 kW with UV-emitting phosphor and an envelope of Wood's glass are used for theatrical and concert displays. Black lights are used in applications in which extraneous visible light must be minimized; mainly to observe fluorescence , the colored glow that many substances give off when exposed to UV light. UVA/UVB emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-keeping.
SHORT-WAVE ULTRAVIOLET LAMPS
9-watt germicidal UV lamp, in compact fluorescent (CF) form factor Commercial germicidal lamp in butcher shop
A shortwave UV lamp can be made using a fluorescent lamp tube with no phosphor coating. These lamps emit ultraviolet light with two peaks in the UVC band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm. The fused quartz glass tube passes the 253 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UVC power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–40 watts of total UV output. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.
Specialized UV gas-discharge lamps containing different gases produce
UV radiation at particular spectral lines for scientific purposes.
Other UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), deuterium arc lamps , mercury-xenon arc lamps , and metal-halide arc lamps .
The excimer lamp , a UV source developed within the last two decades, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet.
A 380 nanometre UV
UVC LEDs are beginning to be used in disinfection and as line sources to replace deuterium lamps in liquid chromatography instruments.
Main article: Excimer laser
Gas lasers , laser diodes and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available which cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6.6 nm, wavelength. Another type of high power gas laser is the excimer laser . They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride (ArF) excimer lasers operating at 193 nm are routinely used in integrated circuit production by photolithography . The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar2* excimer laser.
Direct UV-emitting laser diodes are available at 375 nm. UV diode
lasers have been demonstrated using Ce:LiSAF crystals (cerium -doped
lithium strontium aluminum fluoride), a process developed in the 1990s
Lawrence Livermore National Laboratory
Ultraviolet lasers have applications in industry (laser engraving ), medicine (dermatology , and keratectomy ), chemistry (MALDI ), free air secure communications , computing (optical storage ) and manufacture of integrated circuits.
TUNABLE VACUUM ULTRAVIOLET (VUV) VIA SUM AND DIFFERENCE FREQUENCY MIXING
The vacuum ultraviolet (VUV) band (100–200 nm) can be generated by non-linear 4 wave mixing in gases by sum or difference frequency mixing of 2 or more longer wavelength lasers. The generation is generally done in gasses (e.g. krypton, hydrogen which are two-photon resonant near 193 nm) or metal vapors (e.g. magnesium). By making one of the lasers tunable, the VUV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the VUV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. Difference frequency mixing (lambda1 + lambda2 − lambda3) has an advantage over sum frequency mixing because the phase matching can provide greater tuning. In particular, difference frequency mixing two photons of an ArF (193 nm) excimer laser with a tunable visible or near IR laser in hydrogen or krypton provides resonantly enhanced tunable VUV covering from 100 nm to 200 nm. Practically, the lack of suitable gas/vapor cell window materials above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable VUV wavelengths down to 75 nm was achieved using window-free configurations.
PLASMA AND SYNCHROTRON SOURCES OF EXTREME UV
Lasers have been used to indirectly generate non-coherent extreme UV (EUV) radiation at 13.5 nm for extreme ultraviolet lithography . The EUV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser. This technique does not require a synchrotron, yet can produce UV at the edge of the X-ray spectrum. Synchrotron light sources can also produce all wavelengths of UV, including those at the boundary of the UV and X-ray spectra at 10 nm.
HUMAN HEALTH-RELATED EFFECTS
Further information: Health effects of sun exposure
The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health . Getting too much sun exposure can be harmful, but in moderation is beneficial.
The benefits of UV can outweigh manageable risks. UV light causes the body to produce vitamin D , which is essential for life. The human body needs some UV radiation in order for one to maintain adequate vitamin D levels.
Reasonable exposure to ultraviolet radiation from the sun can be a good source of vitamin D. One minimal erythemal dose of sunlight UV radiation provides the equivalent of about 20,000 IU of vitamin D2, taken as an oral supplement. If an adult's arms and legs are exposed to a half minimal erythemal UV radiation, it is the same as taking 3,000 IU of vitamin D3 through an oral supplement. This exposure of 10–15 minutes, on a frequency of two to three times per week will cause the adult's skin to produce enough vitamin D. It is not necessary to expose the face to the UV, as facial skin provides little vitamin D3. Individuals whose metabolism makes taking oral vitamin D ineffective are able, through exposure to an ultraviolet lamp that emits UV-B radiation, to achieve a 25 (OH) D blood level.
Three benefits of UV exposure are production of vitamin D, improvement in mood, and increased energy.
UVB induces production of vitamin D in the skin at rates of up to 1,000 IUs per minute. This vitamin helps to regulate calcium metabolism (vital for the nervous system and bone health), immunity, cell proliferation, insulin secretion, and blood pressure. In third-world countries, foods fortified with vitamin D are "practically nonexistent." Most people in the world depend on the sun to get vitamin D.
There are not many foods that naturally have vitamin D. Examples are cod liver oil and oily fish. If people cannot get sunlight, then they will need 1,000 IU of vitamin D per day to stay healthy. A person would have to eat oily fish three or four times per week in order to get enough vitamin D from that food source alone.
People with higher levels of vitamin D tend to have lower rates of diabetes, heart disease, and stroke and tend to have lower blood pressure. However, it has been found that vitamin D supplementation does not improve cardiovascular health or metabolism, so the link with vitamin D must be in part indirect. People who get more sun are generally healthier, and also have higher vitamin D levels. It has been found that ultraviolet radiation (even UVA) produces nitric oxide (NO) in the skin, and nitric oxide can lower blood pressure. High blood pressure increases the risk of stroke and heart disease. Although long-term exposure to ultraviolet contributes to non-melanoma skin cancers that are rarely fatal, it has been found in a Danish study that those who get these cancers were less likely to die during the study, and were much less likely to have a heart attack, than those who did not have these cancers.
People in certain situations, such as people with intellectual disabilities and neurodevelopmental disorders who stay inside most of the time have low vitamin D levels. Getting enough vitamin D can help stave off "autoimmune diseases, cardiovascular disease, many types of cancer, dementia, types 1 and 2 diabetes mellitus, and respiratory tract infections."
Fetuses and children who do not get enough vitamin D can suffer from "growth retardation and skeletal deformities."
UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma.
Cardiovascular And Hypertension
Worldwide, one billion people suffer from hypertension. In the U.S., half of the 146 million hypertensive patients don't have their blood pressure under control. In hypertension patients who suffer from vitamin D deficiency, UVB radiation (but not UVA) lowered blood pressure.
Modern pharmaceutical therapy has resulted in an overall reduction in hypertension, particularly in countries with high GDP per capita. A review of blood pressure statistics before these pharmaceuticals were available shows a coherent correlation between high blood pressure and higher latitude. Seasons of the year also impact high blood pressure; BP is lower in the summer months in high latitudes than it is in the winter, when there is less sunlight. Individuals with more sun exposure synthesize more active vitamin D (1,25 di-hydroxy cholecalciferol) from diet or ultraviolet radiation exposure. A combination of lower ultraviolet radiation with insufficient vitamin D in a diet leads to vitamin D deficiency. Individuals whose vitamin D ranks in the lowest quartile have double the all-cause mortality of those who rank in the highest quartile. They are also more likely to suffer from cardiovascular disease, hypertension and organ cancer.
Medical trials have demonstrated that vitamin D supplements do not prevent or treat hypertension or cardiovascular disease, although they can help in skeletal metabolism. Epidemiological and observational studies show indications that exposure to ultraviolet radiation, particularly sunlight, might reduce all-cause mortality and can help reduce cardiovascular disease and hypertension. One hundred years of scientific data has demonstrated that the effect of ultraviolet radiation on human skin is carcinogenic. There is a lack of evidence that this carcinogenic effect, like risks such as smoking or alcohol, is responsible for higher mortality. There are significant archives of studies demonstrating that ultraviolet radiation from sunlight provides measurable health benefits, independent of vitamin D.
Changes in serotonin levels affect how humans act relative to mood and behavior. Measured serotonin is much higher among those who die in summer, rather than winter.
Serotonin is a monoamine neurotransmitter that is thought to provide sensations of happiness, well being and serenity to human beings.
It is thought that serotonin affects a plethora of human bodily functions from anxiety and mood to bowel function to bone density to sexuality. Its importance in human activity continues to be a source of much scientific examination and experimentation.
The amount of the brown pigment melanin in the skin increases after
exposure to UV radiation at moderate levels depending on skin type ;
this is commonly known as a sun tan .
Melanin is an excellent
photoprotectant that absorbs both UVB and UVA radiation and dissipates
the energy as harmless heat, protecting the skin against both direct
"There is no doubt that a little sunlight is good for you!" – World Health Organization
Main article: Ultraviolet light and cancer
In humans, excessive exposure to UV radiation can result in acute and
chronic harmful effects on the eye's dioptric system and retina. The
risk is elevated at high altitudes and people living in high latitude
countries where snow covers the ground right into early summer and sun
positions even at zenith are low, are particularly at risk . Skin, the
circadian and immune systems can also be affected. Ultraviolet
photons harm the
The differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum.". The action spectrum shows that UVA does not cause immediate reaction, but rather UV begins to cause photokeratitis and skin redness (with Caucasians more sensitive) at wavelengths starting near the beginning of the UVB band at 315 nm, and rapidly increasing to 300 nm. The skin and eyes are most sensitive to damage by UV at 265–275 nm, which is in the lower UVC band. At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with so little penetrating the atmosphere. The WHO-standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at a given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UVA and UVB bands. Bioolympics discover UV reaction index to detect the leak of UV light.
Overexposure to UVB radiation not only can cause sunburn but also
some forms of skin cancer . However, the degree of redness and eye
irritation (which are largely not caused by UVA) do not predict the
long-term effects of UV, although they do mirror the direct damage of
All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.
UVB radiation can cause direct
The most deadly form of skin cancer , malignant melanoma , is mostly
In the past, UVA was considered not harmful or less harmful than UVB,
but today it is known to contribute to skin cancer via indirect DNA
damage (free radicals such as reactive oxygen species). UVA can
generate highly reactive chemical intermediates, such as hydroxyl and
oxygen radicals, which in turn can damage DNA. The
UVB photons can cause direct
As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type ) levels of radiation; this is commonly known as a sun tan . The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.
Some sunscreen lotions now include compounds such as titanium dioxide which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone .
Medical organizations recommend that patients protect themselves from UV radiation by using sunscreen . Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage.
The photochemical properties of melanin make it an excellent photoprotectant . However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species may be increased. The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough to cause damage.
In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin. The study indicates that sunscreen must be reapplied within 2 hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.
Aggravation Of Certain Skin Conditions
Ultraviolet radiation can aggravate several skin conditions and diseases, including:
The eye is most sensitive to damage by UV in the lower UVC band at
Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light can reach the eyes from the sides, full-coverage eye protection is usually warranted if there is an increased risk of exposure, as in high-altitude mountaineering. Mountaineers are exposed to higher-than-ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice. Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate , inherently block most UV.
DEGRADATION OF POLYMERS, PIGMENTS AND DYES
Main article: UV degradation UV damaged polypropylene rope (left) and new rope (right)
UV degradation is one form of polymer degradation that affects plastics exposed to sunlight . The problem appears as discoloration or fading, cracking, loss of strength or disintegration. The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.
Sensitive polymers include thermoplastics and speciality fibers like
aramids . UV absorption leads to chain degradation and loss of
strength at sensitive points in the chain structure.
Many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV. Various forms of picture framing glass , including acrylics (plexiglass), laminates, and coatings, offer different degrees of UV (and visible light) protection.
Because of its ability to cause chemical reactions and excite fluorescence in materials, ultraviolet radiation has a number of applications. The following table gives some uses of specific wavelength bands in the UV spectrum
* 13.5 nm:
Extreme ultraviolet lithography
* 30–200 nm:
Photoionization , ultraviolet photoelectron
spectroscopy , standard integrated circuit manufacture by
* 230–365 nm: UV-ID, label tracking, barcodes
* 230–400 nm: Optical sensors , various instrumentation
* 240–280 nm:
Disinfection , decontamination of surfaces and water
Main article: Ultraviolet photography A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers.
Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Photography with wavelengths shorter than 350 nm requires special quartz lenses which do not absorb the radiation. Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.
Photography by reflected ultraviolet radiation is useful for medical,
scientific, and forensic investigations, in applications as widespread
as detecting bruising of skin, alterations of documents, or
restoration work on paintings. Photography of the fluorescence
produced by ultraviolet illumination uses visible wavelengths of
light. Aurora at
In ultraviolet astronomy , measurements are used to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space.
ELECTRICAL AND ELECTRONICS INDUSTRY
EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent (quartz ) window on the top of the chip that allows the UV radiation in.
FLUORESCENT DYE USES
Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be present and causes the colors and whites to appear whiter or more brightly colored.
UV fluorescent dyes that glow in the primary colors are used in paints, papers, and textiles either to enhance color under daylight illumination or to provide special effects when lit with UV lamps. Blacklight paints that contain dyes that glow under UV are used in a number of art and esthetic applications. A bird appears on many Visa credit cards when they are held under a UV light source
To help prevent counterfeiting of currency, or forgery of important documents such as driver's licenses and passports , the paper may include a UV watermark or fluorescent multicolor fibers that are visible under ultraviolet light. Postage stamps are tagged with a phosphor that glows under UV rays to permit automatic detection of the stamp and facing of the letter.
UV fluorescent dyes are used in many applications (for example, biochemistry and forensics ). Some brands of pepper spray will leave an invisible chemical (UV dye) that is not easily washed off on a pepper-sprayed attacker, which would help police identify the attacker later.
In some types of nondestructive testing UV stimulates fluorescent dyes to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (liquid penetrant inspection ) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic particle inspection ).
UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood, and saliva. For example, ejaculated fluids or saliva can be detected by high-power UV sources, irrespective of the structure or colour of the surface the fluid is deposited upon. UV-Vis microspectroscopy is also used to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.
Other applications include the authentication of various collectibles and art, and detecting counterfeit currency. Even materials not specially marked with UV sensitive dyes may have distinctive fluorescence under UV exposure or may fluoresce differently under short-wave versus long-wave ultraviolet.
Enhancing Contrast Of Ink
Using multi-spectral imaging it is possible to read illegible papyrus
, such as the burned papyri of the
Villa of the Papyri or of
Oxyrhynchus , or the
Simple NUV sources can be used to highlight faded iron-based ink on vellum.
After a training exercise involving fake body fluids , a healthcare worker's personal protective equipment is checked with ultraviolet light to find invisible drops of fluids. These fluids could contain deadly viruses or other contamination.
Ultraviolet aids in the detection of organic material deposits that remain on surfaces where periodic cleaning and sanitizing may not have been properly accomplished. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected .
Perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.
UV/VIS spectroscopy is widely used as a technique in chemistry to analyze chemical structure , the most notable one being conjugated systems . UV radiation is often used to excite a given sample where the fluorescent emission is measured with a spectrofluorometer . In biological research, UV radiation is used for quantification of nucleic acids or proteins . A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.
Ultraviolet lamps are also used in analyzing minerals and gems .
In pollution control applications, ultraviolet analyzers are used to detect emissions of nitrogen oxides, sulfur compounds, mercury, and ammonia, for example in the flue gas of fossil-fired power plants. Ultraviolet radiation can detect thin sheens of spilled oil on water, either by the high reflectivity of oil films at UV wavelengths, fluorescence of compounds in oil or by absorbing of UV created by Raman scattering in water.
MATERIAL SCIENCE USES
In general, ultraviolet detectors use either a solid-state device,
such as one based on silicon carbide or aluminium nitride , or a
gas-filled tube as the sensing element. UV detectors that are
sensitive to UV in any part of the spectrum respond to irradiation by
sunlight and artificial light . A burning hydrogen flame, for
instance, radiates strongly in the 185- to 260-nanometer range and
only very weakly in the IR region, whereas a coal fire emits very
weakly in the U
V band yet very strongly at IR wavelengths; thus, a
fire detector that operates using both UV and IR detectors is more
reliable than one with a UV detector alone. Virtually all fires emit
some radiation in the UVC band, whereas the
UV detectors are sensitive to most fires, including hydrocarbons ,
metals, sulfur , hydrogen , hydrazine , and ammonia .
Ultraviolet radiation is used for very fine resolution photolithography , a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The exposure causes chemical reactions to occur in the photoresist. After removal of unwanted photoresist, a pattern determined by the mask remains on the sample. Steps may then be taken to "etch" away, deposit on or otherwise modify areas of the sample where no photoresist remains.
Photolithography is used in the manufacture of semiconductors , integrated circuit components, and printed circuit boards . Photolithography processes used to fabricate electronic integrated circuits presently use 193 nm UV and are experimentally using 13.5 nm UV for extreme ultraviolet lithography .
Electronic components that require clear transparency for light to exit or enter (photovoltaic panels and sensors) can be potted using acrylic resins that are cured using UV energy. The advantages are low VOC emissions and rapid curing. Effects of UV on finished surfaces in 0, 20 and 43 hours.
Certain inks, coatings, and adhesives are formulated with photoinitiators and resins. When exposed to UV light, polymerization occurs, and so the adhesives harden or cure, usually within a few seconds. Applications include glass and plastic bonding, optical fiber coatings, the coating of flooring, UV coating and paper finishes in offset printing , dental fillings, and decorative fingernail "gels".
UV sources for UV curing applications include UV lamps , UV LEDs , and Excimer flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are used, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs can be used for static applications. Small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.
The impact of UV on polymers is used for modification of the (roughness and hydrophobicity ) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet.
UV radiation is useful in preparing low-surface-energy polymers for adhesives. Polymers exposed to UV will oxidize, thus raising the surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger.
Using a catalytic chemical reaction from titanium dioxide and UVC
exposure, oxidation of organic matter converts pathogens , pollens ,
and mold spores into harmless inert byproducts. The cleansing
mechanism of UV is a photochemical process. Contaminants in the indoor
environment are almost entirely organic carbon-based compounds, which
break down when exposed to high-intensity UV at 240 to 280 nm.
Short-wave ultraviolet radiation can destroy
UV has also been shown to reduce gaseous contaminants such as carbon monoxide and VOCs . UV lamps radiating at 184 and 254 nm can remove low concentrations of hydrocarbons and carbon monoxide if the air is recycled between the room and the lamp chamber. This arrangement prevents the introduction of ozone into the treated air. Likewise, air may be treated by passing by a single UV source operating at 184 nm and passed over iron pentaoxide to remove the ozone produced by the UV lamp.
Sterilization And Disinfection
Main article: Ultraviolet germicidal irradiation A low-pressure mercury vapor discharge tube floods the inside of a hood with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.
Ultraviolet lamps are used to sterilize workspaces and tools used in
biology laboratories and medical facilities. Commercially available
low-pressure mercury-vapor lamps emit about 86% of their radiation at
254 nanometers (nm), with 265 nm being the peak germicidal
effectiveness curve. UV at these germicidal wavelengths damage a
UV-C LEDs are relatively new to the commercial market and are gaining in popularity. Due to their monochromatic nature (± 5 nm) these LEDs can target a specific wavelength needed for disinfection. This is especially important knowing that pathogens vary in their sensitivity to specific UV wavelengths. LEDs are mercury free, instant on/off, and have unlimited cycling throughout the day.
Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in municipal drinking water treatment . Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection has been researched for cheaply treating contaminated water using natural sunlight . The UV-A irradiation and increased water temperature kill organisms in the water.
Ultraviolet radiation is used in several food processes to kill unwanted microorganisms . UV can be used to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV absorbance of the juice.
Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 nm . Pulsed light works with xenon flash lamps that can produce flashes several times per second. Disinfection robots use pulsed UV
Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet wavelengths. Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on a yellow to green color under UV illumination, thus assisting in the control of these arachnids. Many birds have patterns in their plumage that are invisible at usual wavelengths but observable in ultraviolet, and the urine and other secretions of some animals, including dogs, cats, and human beings, is much easier to spot with ultraviolet. Urine trails of rodents can be detected by pest control technicians for proper treatment of infested dwellings.
Butterflies use ultraviolet as a communication system for sex recognition and mating behavior. For example, in the Colias eurytheme butterfly, males rely on visual cues to locate and identify females. Instead of using chemical stimuli to find mates, males are attracted to the ultraviolet-reflecting color of female hind wings.
Many insects use the ultraviolet wavelength emissions from celestial
objects as references for flight navigation. A local ultraviolet
emitter will normally disrupt the navigation process and will
eventually attract the flying insect. Entomologist using a UV
light for collecting beetles in
The green fluorescent protein (GFP) is often used in genetics as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.
Ultraviolet traps called bug zappers are used to eliminate various small flying insects. They are attracted to the UV and are killed using an electric shock, or trapped once they come into contact with the device. Different designs of ultraviolet radiation traps are also used by entomologists for collecting nocturnal insects during faunistic survey studies.
Main article: Ultraviolet light therapy
Ultraviolet radiation is helpful in the treatment of skin conditions such as psoriasis and vitiligo . Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralens is an effective treatment for psoriasis . Due to the potential of psoralens to cause damage to the liver , PUVA therapy may be used only a limited number of times over a patient's lifetime.
UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the exposure is needed. However, phototherapy can be effective when used in conjunction with certain topical treatments such as anthralin, coal tar, and vitamin A and D derivatives, or systemic treatments such as methotrexate and Soriatane.
Reptiles need UVB for biosynthesis of vitamin D, and other metabolic processes. Specifically cholecalciferol (vitamin D3), which is needed to for basic cellular / neural functioning as well as the utilization calcium for bone and egg production. The UVA wavelength is also visible to many reptiles and might play a signifiant role in their ability survive in the wild as well as visual communication between individuals. Therefore, in a typical reptile enclosure, a fluorescent UV a/b source (at the proper strength / spectrum for the species), must be available for many captive species to survive. Simple supplementation with cholecalciferol (Vitamin D3) will not be enough as there's a complete biosynthetic pathway that is "leapfrogged" (risks of possible overdoses), the intermediate molecules and metabolites also place important functions in the animals health. Natural sunlight in the right levels is always going to be superior to artificial sources, but this might be possible for keepers in different parts of the world.
It is a known problem that high levels of output of the UVa part of
the spectrum can both cause cellular and
The evolution of early reproductive proteins and enzymes is
attributed in modern models of evolutionary theory to ultraviolet
radiation. UVB causes thymine base pairs next to each other in genetic
sequences to bond together into thymine dimers , a disruption in the
strand that reproductive enzymes cannot copy. This leads to
frameshifting during genetic replication and protein synthesis ,
usually killing the cell. Before formation of the UV-blocking ozone
layer, when early prokaryotes approached the surface of the ocean,
they almost invariably died out. The few that survived had developed
enzymes that monitored the genetic material and removed thymine dimers
by nucleotide excision repair enzymes. Many enzymes and proteins
involved in modern mitosis and meiosis are similar to repair enzymes,
and are believed to be evolved modifications of the enzymes originally
used to overcome
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* v * t * e
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* Gamma rays *